Data saving mode not working at all

Yesterday I noticed image quality was better than usual when browsing with data saving mode ON and image quality set to "Low".
I did reset the saved data counter, and since that moment it is stuck at zero kB, 0%, no matter how much I browse.
Then, I changed settings to "no images", but they are still being loaded and shown!
So something is happening, enabling data saving mode is completely useless now!
I even tried installing Opera Beta, but behavior is the same...
Opera for Android 47.0.2249.129167
Please help.